dict: const pointers to dictionary where possible

This avoids temporaries or ugly casting in the calling code where
const dictionaries are used. Esp. helpful when writing C++ wrappers
for an AVDictionary having const member functions and CTORs with const
references.
Signed-off-by: Roman Fietze <roman.fietze@telemotive.de>
Signed-off-by: Michael Niedermayer <michaelni@gmx.at>

libavutil/dict.c

@@ -35,7 +35,7 @@ int av_dict_count(const AVDictionary *m)
     return m ? m->count : 0;
 }
 
-AVDictionaryEntry *av_dict_get(AVDictionary *m, const char *key,
+AVDictionaryEntry *av_dict_get(const AVDictionary *m, const char *key,
                                const AVDictionaryEntry *prev, int flags)
 {
     unsigned int i, j;
@@ -181,7 +181,7 @@ void av_dict_free(AVDictionary **pm)
     av_freep(pm);
 }
 
-void av_dict_copy(AVDictionary **dst, AVDictionary *src, int flags)
+void av_dict_copy(AVDictionary **dst, const AVDictionary *src, int flags)
 {
     AVDictionaryEntry *t = NULL;
 

libavutil/dict.h

@@ -98,7 +98,7 @@ typedef struct AVDictionary AVDictionary;
  * @return found entry or NULL in case no matching entry was found in the dictionary
  */
 AVDictionaryEntry *
-av_dict_get(AVDictionary *m, const char *key, const AVDictionaryEntry *prev, int flags);
+av_dict_get(const AVDictionary *m, const char *key, const AVDictionaryEntry *prev, int flags);
 
 /**
  * Get number of entries in dictionary.
@@ -148,7 +148,7 @@ int av_dict_parse_string(AVDictionary **pm, const char *str,
  * @param flags flags to use when setting entries in *dst
  * @note metadata is read using the AV_DICT_IGNORE_SUFFIX flag
  */
-void av_dict_copy(AVDictionary **dst, AVDictionary *src, int flags);
+void av_dict_copy(AVDictionary **dst, const AVDictionary *src, int flags);
 
 /**
  * Free all the memory allocated for an AVDictionary struct